This invention relates generally to rotating dynamoelectric machines and, more particularly, to such machines that receive power from a direct current or rectified alternating current power supply and that utilize electronic commutation means. More specifically, the present invention relates to electronically commutated motors and control for use with refrigeration systems and which may be particularly adapted for cooling passenger compartments of vehicles.
As discussed in my prior U.S. Pat. No. 4,015,182, many air conditioning systems employ a vehicle engine for driving a compressor through a suitable belt and pulley interconnection arrangement; thus, the amount of cooling acquired from the air conditioning system is directly tied to the engine operating speed. Therefore, the air conditioning system is generally sized to acquire the desired amount of cooling at low speeds or idle speeds of the vehicle which results in an air conditioning system which is much larger than is necessary to cool the passenger compartment at the normal operating speeds of the vehicle. Further, the compressor represents an added load to the engine causing a decrease in engine output power and a significant reduction in gas mileage.
In such prior art air conditioning systems, the excess cooling obtained when the vehicle is operating at normal running speeds may be controlled by cycling a compressor in an "on and off" manner, in accordance with temperature. This on and off cycling may be accomplished by periodically engaging and disengaging a mechanical connection, for example, a clutch connected between the engine and the compressor. However, such on and off type operation of the compressor causes a substantial strain on the mechanical components interconnecting the vehicle engine and compressor, and can cause substantial variance in engine speed which is particularly noticeable in vehicles having smaller sized engines.
In an attempt to eliminate on and off cycling of a compressor in a vehicular air conditioning system, some prior art systems have included a by-pass arrangement whereby excess cooling capacity is negated by allowing refrigerant to by-pass the evaporator so as to acquire a modulated cooling system rather than an on and off cycling system. However, such systems may be subjected to very high pressure differentials, thus increasing the likelihood of refrigerant leakage. Other prior art systems have attempted to compensate for excess cooling capacity within the air conditioning system by heating the cooling air being moved into the passenger compartment. As is readily apparent, such modulated control approaches and systems are very inefficient in that energy is being expended by the vehicle in creating the cooling capacity within the air conditioning system and then such energy is being wasted by either by-passing the evaporator or heating the air before movement into the passenger compartment.
In my prior U.S. Pat. No. 4,015,182, I disclosed, among other things, an air conditioning system employing an electronically commutated motor which eliminated and/or minimized many of the problems discussed hereinabove. For example, an air conditioning system employing an electronically commutated motor was disclosed which eliminated mechanical interconnections between the compressor and the engine of the vehicle so that the compressor speed was not dependent on the operating speed of the vehicle engine. Therefore, in addition to eliminating many of the mechanical problems associated with such interconnections, the disclosed arrangement allows design of a cooling system independent of engine speed considerations, and therefore, eliminates the need for drastic and wasteful oversizing of a cooling system. In another aspect of my prior patent, I disclosed an arrangement for controlling a refrigertion system so as to maintain a compartment at a desired operating temperature. The arrangement involves, among other things, controlling the amount of cooling of a refrigeration system by varying the energization level of stator windings in an electronically commutated motor.
However, it would be desirable to develop an improved electronically commutated motor and control arrangement for use with a refrigeration system which would improve temperature control within the compartment being cooled, improve operating life of system components, and at the same time, improve operating efficiency for the system. Temperature within a compartment can be controlled by cycling a compressor and its driving motor in an on-off manner, but to acquire relatively accurate control, the compressor and motor must be cycled quite often to keep the temperature within a narrow control span. However, frequent starting and stopping tends to decrease the operating life of the system. Each start-up of a brushless DC motor causes relatively high currents to be fed to the motor windings, thereby causing heating of electrical power driving components and the motor itself, and also, causing greater power losses within the motor windings. Further, it is believed that an energy loss of as much as 10-15% may occur when a compressor is cycled on and off at particular cycle rates. This significant energy loss is believed to be due to the migration of liquid refrigerant to ineffective cooling locations within the refrigeration system. For example, liquid refrigerant may migrate, during the off condition of the compressor, to locations beyond the evaporator, and upon subsequent restart of the compressor, the liquid refrigerant vaporizes outside the evaporator where no cooling effect is acquired as a result of such vaporization. Thus, it would be desirable to develop a control arrangement whereby the temperature within a compartment could be more accurately controlled and whereby the refrigeration system could be continuously modulated or controlled.
Still further, it would be desirable to develop an electronically commutated motor and control arrangement for use with a refrigeration system which would be responsive to different cooling demands within a compartment being cooled by the system. In a refrigeration system utilized to cool the passenger compartment of a vehicle, the compressor is typically operated to maintain a predetermined temperature at a location on an evaporator of the system. However, cooling demands upon such systems vary drastically. For example, if the vehicle has been parked in the hot sun, a great degree of cooling is desired to quickly bring the passenger compartment temperature to a comfortable level. Therefore, it would be desirable to develop a control arrangemnet which would automatically respond to varying cooling demands within the passenger compartment for automatically varying the degree of cooling of the system.
Furthermore, refrigeration systems in which a compressor is driven by an electric motor often have a lubricating pump arrangement for lubricating bearings of the motor. However, many of these pumping arragements are only effective at certain operating speeds of a motor; thus, it would be desirable to develop a control arrangement which would assure proper lubrication of motor bearings.
Moreover, it would be desirable to develop an electronically commutated motor and control arrangement for use with a refrigeration system which would be responsive to common failures or abnormal conditions within the system such as, for example, loss of refrigerant charge, a faulty temperature sensing element and/or evaporator freeze-up, and which would control motor operation when such failures occur so as to prevent damage to the motor and its power circuitry.
Accordingly, it is a general object of the present invention to develop new and improved brushless DC motor and control arrangements for use with refrigeration systems.
More specifically, an object of the present invention is to develop new and improved brushless DC motor and control arrangements which are particularly adaptable for controlling vehicular air conditioning systems.
Another object of the present invention is to develop new and improved electronically commutated motor and control arrangements for use with refrigeration systems which provide improved temperature control within compartments being cooled and which improve the operating efficiencies of the systems.
Still another object of the present invention is to develop new and improved control arrangements which are responsive to different cooling demands of compartments being cooled by refrigeration systems and which automatically vary the degree of cooling of the systems in accordance with such demands.
Yet another object of the present invention is to provide new and improved electronically commutated motor and control arrangements which control motor operating speed so as to assure proper lubrication of bearings of the motors.
A further object of the present invention is to provide new and improved electronically commutated motor and control arrangements for use with refrigeration systems which are responsive to common failures or abnormal conditions within the systems for controlling motor operation so as to prevent damage to the motors and their power circuitry.
A still further object of the present invention is to provide new and improved methods of operating refrigeration systems utilizing electronically commutated motors which improve temperature control within compartments being cooled and which improve operating efficiencies of the systems.
Yet a further object of the present invention is to provide new and improved methods of operating refrigeration systems utilizing electronically commutated motors which prevent damage to the motors and their circuitry when failures or abnormal conditions occur within the system.